The neutrophil polymorphonuclear leukocyte (PMN) is an early arriver at sites of tissue injury and repair. Its primary role is the prevention of infection. This is accomplished by three motile functions: chemotaxis, phagocytosis and degranulation. Biochemical evidence suggests that cell movement is effected by an actinmyosin contractile cytoskeleton. One is therefore led to ask: What is the mechanical relationship of the cytoskeleton to cell motility? To answer this question, we have established two goals: 1. Determine the ultrastructural relationship of the actin and myosin filaments in pure protein motile models. 2. Identify the actin and myosin cytoskeletal elements in intact PMNs at the electron microscope level using ferritin labeled antibodies. The results should allow us to establish the identity, localization, and dynamic alterations of the cytoskeletal elements in PMNs. The immediate applicability of this work will be to the analysis of leukocyte chemotaxis and phagocytosis. It is hoped that these studies will help lay a foundation for understanding fibroblast migration and contraction during wound repair.